According to the U.S. Department of Labor and Occupational Safety & Health Administration (OSHA), each year there are approximately 10,000 incidents of accidental electric shock. While not all electrocutions are fatal, about 9% or approximately 900 are. This statistic does not include the many thousands of unreported accidental electric incidents. By the time they reach adulthood, most people have been accidentally shocked by accidentally touching an electrically charged wire, a faulty light switch, a faulty lamp, plugging in an electrical device in a damp environment or from ground fault situation. Electrical shock is not only an uncomfortable experience, but it may also cause very painful burns or even death.
Ground fault interrupters (GFI) or ground fault circuit interrupters (GFCI) are designed to protect from electrical shock by interrupting a circuit when there is a difference in the currents in the “hot” and neutral wires. Such a difference indicates that an abnormal diversion of current from the “hot” wire is occurring. Such a current might be flowing in the ground wire, such as a leakage current from a motor or from capacitors. More importantly, that current diversion may be occurring because a person has come into contact with the “hot” wire and is being shocked. When a circuit is functioning normally, all of the return current from an appliance flows through the neutral wire, so the presence of a difference between “hot” and neutral currents represents a malfunction which in some circumstances could produce a dangerous or even lethal shock hazard.
Because of the great sensitivity of the detection of current differences, GFIs are prone to nuisance tripping in certain applications. A rather common practice in some areas is to have a freezer on the carport, and carport receptacles are sometimes wired with GFIs. Under moist conditions you can sometimes get enough leakage current to trip the GFI, and persons come back to find their freezer thawed out. A necessary safety precaution in bathrooms and near pools, they are sometimes quite troublesome in outdoor applications where reliable power is needed.
Moreover, the protective circuitry in a GFI is vulnerable to voltage spikes such as those caused by lightning and high-voltage switching. Thus, the GFI may eventually fail to provide ground-fault protection while still providing power for tools and appliances. With the wide use of portable tools on construction sites, the use of flexible cords often becomes necessary. Hazards are created when cords, cord connectors, receptacles, and cord-connected equipment are improperly used and maintained. Generally, flexible cords are more vulnerable to damage than is fixed wiring. A flexible cord may be damaged by activities on the job, by door or window edges, by staples or fastenings, by abrasion from adjacent materials, or simply by aging. If the electrical conductors of the flexible cord become exposed, and the GFI fails to provide ground-fault protection there is a danger of shocks, burns, or fire. A frequent hazard on a construction site is a cord assembly with improperly connected terminals.
When a cord connector is wet, hazardous leakage can occur to the equipment grounding conductor and to humans who pick up that connector if they also provide a path to ground. Such leakage is not limited to the face of the connector but also develops at any wetted portion of it. Typically, when the leakage current of tools is below 1 ampere, and the grounding conductor has a low resistance, no shock should be perceived. However, when the resistance of the equipment grounding conductor increase, the current through the body may also increase. Thus, if the resistance of the equipment grounding conductor is significantly greater than 1 ohm, tools with even small leakages become hazardous. Such dangerous situations may also occur if an electric motor, used in irrigation for example, is suddenly immersed in several inches of water and the GFI fails to provide ground-fault protection, then a worker coming into contact with the motor or the water source would be shocked, possibly fatally, and the motor would stop functioning.
Accordingly, there is a need for addressing the problems noted above and others previously experienced.